Protective relay system



O'. 1.-BLISS.

PROTECTIVE RELAY SYSTEM.

APPLICATION meu xuLY 29,1915.

1,3 10,1821 Patented July 22, 1919.

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ADEVILLE J'. BLISS, 0F CHICAGO, ILLINOIS.

PROTECTIVE RELAY SYSTEM,

iipeclcaton of Letters Iatcnt. l Patenteii July 22, 1919.

Application led July 29, 1918. Serial No. 247,133.

To all ywhom t may concern.'

Be it known that I, ORVILLE J. Buss; a citizen of the United States, residing at Chicago, in the: county of Cook and State ot' Illinois, have 'invented a certain new and useful Improvement in Protective Relay Systems, of which the' following is a full, clear, concise, and exact description,-refer ence being had to the accompanying drawings, forming-a. part of this specification.

My invention relates to protective devicesfor electrical apparatus and more particularly to a protective relay system for disconnecting under abnormal conditions the electrical apparatus to be controlled. In such systems it is customary to provide a switch at each end of the cable or feeder to be protected or at the terminals-that is.J upon each side. of. the generator or other piece of apparatus to be protected and to control the operation of these disconnecting switches by relays related serially to the line or other piece of apparatus. It' is. customary to provide series transformers at each end of the feeder, cable or other piece of apparatus and to connect the relays in a closed circuit in series with the secondaries of the transformers by Ameans of pilot Wires.

Heretofore these transformers have been so connected that the potentials generated either during normal operation or u on the occurrence of a through fault, are opposed to each other so that no current shall flow at such times and consequently the relays are supposed to remain inactive, until a fault in the line results in unequal volta-ge or cumulative voltages. i

In practice it has been found that such a relay system is subject to serious defects,' which impair the effectiveness of Particularly one fault. of suchthe same. opposed voltage systems which is very noticeable upon the occurrence of a through fa.ult,that is a fault occurring ibeyond the particular section orA piece of apparatus under consideration-is the failure to main'- tain a balance of voltages. In suchfcase a very heavy current flows through the feeder or other piece of apparatus under consideration, with the result that the voltage on the secondaries of the serres transformers may rise to a .dangerously high value. The oppo- 'to the lcapacity of the pilot wires.

sition of these voltages to .each other for all values of current which may liow through the feeder or other -piece of apparatus, re-

4quiresthe characteristics of the transforiners to fbe identical over a very Wide range. If the characteristics are Adifferent at any point, current will flow inthe closed relay circuits and the relays maybe operated when the saine is not desirable. 'Where a l through fault occurs under the above conditions4 the feeder or cable or'other piece of apparatus will erroneously he cut out of the circuit when the same is not required and a considerable part of the system may be out eti' when all that is necessary is that the defectiveline or piece of apparatus be dis connected. l

Even 'if the characteristics of the transformers'be near enough alike not to'trip out the switches, the condition of balanced voltage permits the voltage at the terminals of the secondaries to risetc abnormally high values upon the occurrence of the through fault, as the condition of the series transformers is then substantially the saine es upon open circuit. l

The condition of opposed voltage tends to 'cause a distorted Wave. shapeunless the two transformers are exactly alike in this char acteristic.

In a balanced system of this type it has beenI found to be substantially impossible tofifiiviate the current which will flow, due This current may rise to high enough value to trip hut the switches when the saine is not desirable. -This condition is aggravated by the occurrence of a. through fault.

The diiiculty of charging or capacity curient has been found to be veryserious and numerous expedients have 'beentried by thc prior ait to overcome the same.

A further defect of the balanced voltage systein resides in the condition which would be caused by an open pilot .ivire It one of the pilot wires were interrupted in a balanced voltage protective system the system ,Would become inoperative and would not trip out the switches under any condition.

Iy invention aims to provide a system of relays balanced by current flow. Instead of employing such a c'onnection'o current transformers as will result in opposed voltages for through fault conditions and additive voltage for internal fault condition, I reverse .-tlie relation and employ such a connection as will produce balanced voltage only upon the occurrence of interna] fault conditions and additive voltages upon the occurrence of a through fault/condition.

By this arrangement the disadvantages above pointed out are obviated or become of no ii'i'iportance.

I employ differential tripping relays,` preferably of the plunger type, which have tivo windings through Which the current flows upon the occurrence of a through fault in such direction as to neutralize the respective` magnetic effects. `The neutralization might, of course, be accomplishedv otherwise.

I employ for three-phase systems a cur-v rent transformer in each phase. The secondaries are connected together and the terminals connected `to ground by common These secondaries which are connected Vtogether in parallel normally maintain a circulating current which has no effect upon the relay circuit. In one of the leads to ground I connect the primary of a current transformer,` the secondary of which is connected to a di lferenti'al relay and to the pilot circuit. A resistance equivalent to the resistance of one pilot wire is connecten in series with one winding of each of the differential relays and these relay windings with resistances in Series are connected each in a bridge across the terminals of the adjacent transformer second aries. The arrangement ot current transformers may be varied, as may other features of the syst-em, as my invention is broadly new as tothe employment of current iiow for maintaining a condition of balance as distinguished from employing opposed Vvoltages to maintain a condition o'l balance. It will be appreciated that the normal circulatingr current through the secondaiies of the three current transformers holds the system in a balanced condition during .the normal operation of the three phase system. The same method of operation may be employed in a single-phase tem; that is by employing a transformer inv each lead a circulating current may be maintained in the seconda-ries of the transformers. Or if desired,the flow of current may normallyr occur through the pilot wires and relays. This latter is less desirable because of the resistance of the relays and the pilot circuit.

In order to teach those skilled in the art more particularly of the nature and scope of my invention and the fpreferred manner of embodying and practising thensnme, 'L

system in the condition o a through ault;

Fig. 3 is a diagram similar to Fig. 1,

. showing -a` fault occurring on one phase of the feeder to be protected;

Fig. 4 is a diagram of a modification of the manner of connecting the forniers with the pilot wires;

Fig. 5 is asimilar .fragmentary diagram of a modification of the arrangement for connecting the current transformer with the.

closed pilot system; and

series trans- Fig'. 6 is a further lmodification in which the secondary winding of the series transformer of the closed pilot system is directly mounted upon a transformer.

I have shown in Fig. 1 adiagram illushas Athree leads', 1, 2 and 3, in a typical invention;l In'this'case the cable C which core of the common current sie has three leads, 1, 2 an'dAB, ,ina typical f 3-phase installation, is the'piece of apparatus or line to be controlled. This cable is a feeder between the powerl busB, and the distributing bus B2. The power bus B, is

connected by means of the line L, to a suitable source of power. The bus B2 is connccted to various distributing lines, of which the line L2 is typical. The' cableV C'tlius forms a feeder between the power bus B, and the distributing bus B2. Automatic disconnecting-switches S, and S2 control a connection of the feeder C with the buses B, and B2. These switches are of the automatic trippingtype and the tripping of the same is controlled by the relays R, and R2 respectively. The relays are of the plunger type, having the two windings 4, 5 and 6, .7 respectively. y

At each end of the cable C I provide the group or bank of series' transformers T, and

T2 of which the secondaries 8, 9,'10 and 11,

12, 1?). are connected together respectively and the common connections are grounded by means of the wires 14, 15 and 16, 17 i'espectively. In the ground connections 14' and 16 I provide the series transformers Q, and Q respectively. The primary windings of these transformers are connected in series with the round connections l14 and 16.

means of the pilot wires 22,23.' The wind; ings 5 and 7 of the relays R, and Byars al's'o f connected in series in this closed circuit. The di'erential coils Land 6 are bridged across the terminals of lthe transformer seci ondaries 20 and21 respectively.1- Infserier* l12;0 The secont aries of' these vtransformers .are "j 'Q connected together in a closed circuit by these Vresistances being of substantially the vstime value-as the resistance of one of the 5 pilot wires 22 and 23.

. -is only a circulating current and T2, the external Aresult of indicated in Fig.

assumed to take,

Normally no current owsin the ground connitions lei-and 16, respectively, as there v through the secundarios of the series transformers T1 "i which is substantially zero. Any small unbalai'ice which may cause a current How through these leads will be insufiiicnt to cause o ration of the differential relays R, and 2. For' all conditions of balance ci' unbalance in the load of the three phases the flow of cur- -rent in the secondaries of the transformers T2. and T2 is neutralized and no current flows in the ground connections 14 and 16.

In the eventof a through fault, as indicated at X in Fig. 2, the relays will not be tripped out as this fault should be handled by itself by "protective apparatus on the line L2 so as to prevent interruption of the service supplied 2, by means of the arrows, the direction which the current may .be both in the phase' and the aifected parts. The representation of di- -rectioii of current flow in the secondary of each transformer is merely diagrammatic winding y and is consistentlyv shown as in the saine as current in the primary. As a direction fault between phases will eventually be developed into a fault. to ground, the system will operate properly in either case.

Assuming that current is flowing in the direction indicated by the arrow adjacent the wire 3. we may assume that current will be caused to flow similarly in the grounded leads 1l and 16, as indicated byV the arrows ad jacent thereto. These currents flowing through the primaries 1S and 19 of the transformers Q, and Q2 will ers so that current will tend to ilow upward in the winding 20 and downward in the 2l with the result that there is a current flow as indicated by the arrows adjacent thc pilot wires 22 and 23 which circulates through the secondaries of the transformers and through the windings 5 and 7 of the relays R, and R2. At the same time a current will flow downward in the winding 4 and resistance lV, and upward in'the relay winding 6 and resistance 72 diie to these respective parts being bridged across the respectivo. ers. lhecurrent which Hows through the bridged relay coils 4 and 6 is substantially rqual to the current which flows in series through the relay coils 5 and 7. AThis is for the reason that th potentials of the windings 20 and 21 are substantially equal from the bus4 B2. I Vhave grows indicating the directions 0 impress volt- 'ages upon thesecondaries of the transforme' I the transformer Q,

secondaries of the transformand because the resistances W1 and W2'. are

made each substantially equal totherei 2 sistance of a pilot wire. As equal currents ,flow inthe windings' 4 and-5' andin opposite directions, the relay will not be operated. The same is true as to the` relay R2.

unbalance will be insufficient to operate tl'ie opposition tozthmniagnctic relays. As the E. M. :F.s .of the transformer windings 20 and 21 have the same hase relation and areconnected together y a closed circuit of relatively low; resistance, through which current; flows, unduly high potentials are not developed.A

' l pon the occurrence of a fault within the cab-le C,- as indicated 'in Fig. 3 at'the point X, the relays R,l and R2 trip the switchesr Sl and S2 cutting out the cable. 'I have added the appro riate arthe curisnt of the fault X to ground, as indicated by the arrows adjacent the wire 3, This causes current 'to flow in the grounded leads 14 and 16 and'through the primaries of the transformers@1 aiidxQ2, as indicated by the arrows adjacent said wires. Due to the current flowing through the riniaiy windings, potentials will be created) at the secondary windings 20 and 21, but will be in opposition to each other, as indicated by the arrows near the pilot Wire 22. As a consequence,

4 and 6 is effective to trip the relays and'R2 thereby causing the S2. to disconnect the cable.

It is not essential that current should dow into the fault X from each end, as it may be assumed that current will flow only from the leftof the fault X into said fault, so'that will be energized. In such event, current will ilow from the upper switches S1 and these potentials which I have placed? will operate to flow. Current will flow from each side terminal of the ,transformer winding 20 in f the proportion of 3 part-s through the Winding 4 and the resistance W, and one part through the relay Winding 5, pilot wire'22, relay winding 7 of relay R2, thence through rela-y winding 6, resistance 4W2 and-through the pilot Wire 23. However, the current flowing through the windings 6 and 7 of the relay R2 flows through these windings in series and is therefore additive. The result at tie relay R namely,

is eguivalent to the result which is produced the magnetic effect siiiglerelay winding. As a result, both re- -laysrltl and R2 are operated to trip out the switches Sl and S2.

The above explanation will also make clear that the systexn will operate to disconnect-a vcablewhicl'i-ha's a fault' and which' the ilot wiresjshould become broken. Uli

der'no condition is the opposition of' the relaytransfrmer's equivalent to open circuit as with the-balanced voltage system. Even with exact opposition on the pilot circuit, vtherefis still acomparativel'- low impedance circuit'ffor each trans ormer through the bridged'relay coils 4 and 6 with their 'series resistance. Therefore, Wave shape distortions, capacity eects and high potentials occur in a relatively ismall degree and then only'under conditions when this is of no importance. n

The relay which I have shown being of the plunger type will reset itself and thus will always be in condition'to operate whenever the switch `is closed.-A The ,relay may or may not be of the self-resetting type as desired. The operationfof the relay and the tripping of the switch at one end of a' line beforethe relay at the other end of the line has acted will not prevent the relay at the other end from tripping its'switch. I

In tests which I have conducted, I have employed for the transformers T, and T,

current transformers of the ratio of 5 to l, and have employed for the transformers Q1 and Q2 current transformers oli-.aV ratio of 2 to 1. The Yrelays which I employed are of the instantaneous plunger type relays wound with 2% ampercs differential coils. The pilot circuitwas operated over conductors' which are the equivalent to v5 miles olli' No. 12 duplex copper conductors. 1

- It will be apparent to those skilled in the art that the manner of. connecting the closed relay circuit i'n series'relation with the line or other piece of apparatus to be controlled, may beyaried. I have shown modifications in 4, 5 and 6. In the modification shown in Fig. tithe transformers T, are connected at one terminal of, each individually to. ground, and the other terminal( is'connected through a' coil 25 and toground.

The coils 25 are wound upon a common magnetic core 26 which"irrturn is interlinked with the' transformer winding 27, `which 'con responds with the winding 2O shown in Figs.

1,2and'3.'

Theoperation-of this modification -will be ap arent `from the previous description. A n Fig'. '51 I have shown vthe magnetic core be dispensed with and the lwindin 31 as common to the conductors and 3 ot the cable or line to be controlled. The

winding 30 is connected tothe primary 28 of the current transformer Q, which links the lines l, 2 and 3 with the closed pilot circuit.

The transformer windings 30 and '2S may be (placed directly upon the magnetic corejl, if i' esired, as shown 1n 6. In Figs. 5 and 6 there is no circulating current between' the power circuit and the pilot circuit but this 1s replaced by a circulating magnetic flax in the core 31.

` I do not intend to be limited to thc precise details of construction shown and described.

1. In combination, a. pair of relays, a pair transformer .vindings connected to said relays and pilot wires, the electro-motive forces of saidrtrausiormer windings being normally additiveto cause current to flow through the pilot. wir and relays.

2. ln combination, a conductor, a pair of relays, a air of )ilot wires connect-ing said relays an trans ormer windings connected to said relays and to said pilot wires', said relayshaving means subjected to current Low y said transformer windings to innin-4 tain the relays inoperative on through fault conditions, said relays being subjected to additive volta-ges of the rtransforn'ier Windings upon normal current flow in the convof pilot wires connecting said relays andV ductor or u on through fault conditions,

and being su ject to opposed'voltages upon internal fault conditions.

3. In combination, a three-phase line, a

series transformer at each end of the line in each phase, said windings ateachend of the line being connected in parallel, a transformer connected in series with said parallel forces additiveand relaysconnected to said secondaries and to-said pilot wires, said relays having differential windings: 'balfmcedfv by current flow for through fault conditions. 4. In com'binetifm, a line, a'pnir of rel: ys,

cach relay comprising a pair ofdifl'crentia windings of substantially equal resistamfe,1

a pair'of pilot wires, one of said wires being connected to one-terminal of one windingof cach relay, the other terminal of said one winding of each relay beingconnected to.' one tern-unal of the second windingof each relay, said windingsfhaving opposed mab-.-

net-ie effects, a resistance for' each relay, each said resistance 'being connected to the other terminal of said Second windingr of each relay, a transformer winding for eachrelay, each transformer winding' being serially reformer winding`v being connected to the con-1 nectio'n between the relay-windings and the 1li-tedio the une, ne terminal of each mils;

other terminal of each-transformer winding'- being connected to the resistance 'of relay, the second pilot wire being joined to winding and its adjacent resistance; j 5. ln combination, a l1ne,' 'a'pa;r of' re;

lays, euch relay comprising a' pair, ofdiffeb' Y ential windings of su'bstantislly'equnlgresistance, a pair of pilot Wires, one ofJsaid wires being connected to oneA terminal of-one winding of each relay, the other terminel'of said one Winding of each relay being con- 'not-tedio one terminal of the second Winding of each relay, said windings havingopposed xnagnetic'cffects, n insistance for each relay, euchvv seid resistance being connected to the other'tcrminnl of said second winding of each relay, e transformer Winding for each relay, euch transformer winding -being serially rela-ted to the line, one terminal of each transformer YWinding being connected to the connection between the relay windings and the other terminal of each transformer winding being connected to the resistance of each relay, tliesecond pilot wire being joined to'th'e connection 'between each transformer winding and its ndJncent resistance, said pilot` Wires being of substantially equa-l resistance, euch said resistancebeing substan-v tially equal to thel resistance pilot wires.

6. In combination, an electrical device to be controlled, said device having terminals :it cach side thereof, n. transformer winding of one of said serially related to said device adjacent eachterminal of the/device, switching ineens for disconnecting Said terin1nels,- t relay for euch tinnsfornier Winding, said'releys having diiierential windings, pilot wires connecting the transformer windings together with their electro-motive forces additive to maintain a` normal flow of current due to said additive electromotivc forces, said relays having each one Winding connected in series with the pilot -wire's and one Winding in bridge of seid ilot wires, the magnetic effect of said Win ings of each relay being normally opposed to prevent operation of the. relay. v

7. Incombination, e conductor having a switch at each endethereof, a air o'f relays eachJ 'controlling one 'of said switches, a transformer winding for each relay .serially rela-ted to said Conductor; a pair offpilot wires connecting said transformer windings in -series with their electro-motive forces additive to maintain n. circulation of current on through fault. conditions, said relays llaving differential operating coils of substitutially equal effect, one winding of cach'reelw l current, one v vindin wires andthe other 4winding being connected in bridge vof said pilot-Wires.v

transformer winding for each relayserially grelatedf to 'said conductor, a pairof ilot- Wires' connecting said transformer win ings -in series with-their electro-motive forces additive to maintain fr circulation of current on the occurrence of` through fault conditions', said relays having differential operating coils of substantially equal etlect, one

`Winding of each'relay being connected in series with the -pilot Wires and the other Winding being connected in bridgeof said pilot wires, and a resistance connected in the .bridge with 'said relaywindin for balancing t e-.current flow in the win ings of each relay.

9. In combination, a conductor having terminels, a transformer Winding ad'acent each 8. In combination, a. conductor having a. .switcligat each end thereof, a pair of re- :lays each controlling one of said switches, a

the connection between each transformer termina-l of said-conductor, sai windings being seriell related to seid conductor,` a rela for eee transformer winding, saidrelay aving differential windings of substantially equalele'ctrical dimensions, a'pair of 'i pilot wires connecting said transformer windings with the electro-motive forces additive to maintain a normal circulation of' of each rela f being connected in serieswith the pilot wires and the other windings of each relay being connected in bridge of said pilot Wires and a. resistance substantially equal to the'resistance of one pilotv wire connected in each bridge only. I

l0. In combination, anelectrical device to be controlled, transformer windings serially related to said device and' located adjacent the terminals of the device, switching means for saidterminals, a pair of relays having differential windings, said relays control'- ling said switching means, pilot wires connecting said relays in a closed series circuit, the connections of said relays said transformer windings and said pilot wires being each end of the feeder, a, relay for controlling each switch, pilot wires connecting said relays in a closed circuit, transformer windings included serially in said closed cicuitat each end of the feeder, said transformer feeder, the electromotive force of said transformer windings being additive to cause 1current to flownormally 'in the. closed circuit.

-windings being serially related to s'aid each switch, and a series transformer for l in a closed circuit Vwith the relays with their electromot'ive forces additive, said relays` having means for preventing a flow of eurrent inthe feeder' due Ato a through fault from Aoperating said relays.

13.` In combination, a feeder, a switch at l each end of the feeder, arelay controlling each switch, a series transformer winding for r ,ich relay, saidwindings being serially relatedA to the feeder, and being connected in a closed circuit with the relays with their electromot-ive forces additive for a through fault condition, said relays comprising each a differential winding.

14. In combination, a line, a switch at .each end of the line, a relayv for each switch, Said relays each havingdiii'erential windings, a series transfornier'winding for each relay, said transformer winding being serially related to the line with electro-motive forces additive, pilot wires connecting one winding of each relay 1n series with both transformer windings and means connecting the other winding of each relay in parallel across a portion of said closed circuit.

In combination, a line, a switch at Y `each .end of the line, a relay controlling each switch, a series transformer winding foreach relay, vsaid relays each having a pair of windings, means connecting the transformer windings and one of the relay ioA windings of each relay in -a closed series eircuitwith the electro-motive forces of the transformer windings additivca and means connecting` the other windings of said re-4 lays in 4bridge across the terminals of said 'transformer windings respectively.

16. In combination, a, line, a switch at each end of the line, a relay controlling each switch, a series transformer winding for each relay, said relays each having a pair Iof windings, means connecting the transformer windings and one of therelay windings of each' relay in closed series circuit and `means connecting the .other Awindings'of said relays in bridge across' the terminals of said 'transformer windings respectively, and a' resistance in series with. each of the bridged relay windings only.

17. In combination, a line, a switch at eaclrendjof the line, a relay controlling each switch,- a series transformer serially related to the line adjacent each switch, said transformer having secondary windings, said relays each having a pair of differential windings,pilot wires connecting the secondaries of the transformers in` 'a closed circuit with one winding of each-relay, the

each transformer, respectively, and resistances in series with the latter windings only, said resistances being each equivalent to the resistance of one pilot wire. I

18. In a three-phase system, a three-phase line, a switch at each end of the line, a relay controlling each switch, a series transformer in each phase of the line adjacent each end, the secondaries of said series transformers at each end of the line being connected together and to a common return, a pair of series transformers common to the transformers of each phase, said commen transformers being connected in series with the common return, a pair of pilot wires connecting the seccndaries of the common transformers in a closed .series circuit with electro-motive forces additive, said relays having each a winding connected in series in said'closed circuit/V.v

19. In a three-phase system, a three-phase line, a switch at each end of the line, series Vtransformersserially related at eac. phase, .one adjacent each end of the line, a pair of pilot wires connecting the Asecondaries of the transformers .in a closed series' circuit with their electro-motive forces additive upon the occurrence of a through fault, and relays connected in series in said closed circuit, said relays controlling said switch, said relays having each a pair of di'erential windings. i f

90. In combination, a line' to be controlled, switches for the ends of the line differential relays controlling the switches, pilot wires connect-ing windings of the relays in a closed circuit, and transformer windings scriallyrrelated to the line with electro- In witness whereof I hereunto subscribe my name this 26th day of July, 1918.

QRVILLE Jj'iiiss.

,1 0 0 governing the 

